Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

2. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-77.7°C

-56.6°C

3. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will evaporate

Water will never evaporate

A gas will never liquefy

4. The boiling point of ammonia is

-10.5°C

-77.7°C

-33.3°C

-30°C

5. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

Zero

None of these

Positive

6. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

2.33

1.33

4.33

7. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Freon

Carbon dioxide

Brine

8. Most thermostatic expansion valves are set for a superheat of

15°C

20°C

10°C

5°C

9. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

10. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

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11. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Condenser

Absorber

Evaporator

12. The operating pressure for refrigerating units using R-12 as a refrigerant is

2 bar

8 bar

30 bar

15 bar

13. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

14. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 9

1: 3

9: 1

15. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Sub-cooling or under-cooling

Normal cooling

Super-cooling

16. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Any one of the above

Equal to unity

Always more than unity

17. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Stirling

Ericson

Carnot

18. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

19. For obtaining high COP, the pressure range of compressor should be

Optimum

Any value

High

Low

20. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

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21. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Evaporator and compressor

Receiver and evaporator

Condenser and receiver

22. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Axial

Centrifugal

Piston type reciprocating

23. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

24. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

25. Rating of a domestic refrigerator is of the order of

0.1 ton

5 tons

10 tons

40 tons

26. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

27. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

28. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

At critical Temperature

Near critical temperature of refrigerant

Above critical temperature

29. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

30. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

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31. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

32. Freon group of refrigerants are

Non-inflammable and toxic

Inflammable

Toxic

Nontoxic and non-inflammable

33. The curved lines on a psychrometric chart indicates

Dew point temperature

Relative humidity

Dry bulb temperature

Wet bulb temperature

34. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

35. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Large latent heat

High risibility with oil

Good electrical conductor

36. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Rankine

Reversed Carnot

Rankine

37. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Collect vapours

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

38. A bootstrap air cooling system has

Three heat exchangers

Two heat exchangers

Four heat exchangers

One heat exchanger

39. The capillary tube, as an expansion device, is used in

All of these

Domestic refrigerators

Water coolers

Room air conditioners

40. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.67

0.4

0.376

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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